Optical element and light-emitting device

ABSTRACT

Provided are an optical element and a light-emitting device with which the illuminated area can be expanded in spite of a small light-emitting area, and that also enable the device to be downsize. The light-emitting device is equipped with sheet-like light-guide sections (a first light-guide section and a second light-guiding section) for guiding light, and a light-emitting member for emitting light. The second light-guide section has a prism section with a saw tooth-like cross-section for changing the direction of the light guided to one of its surfaces. In the prism section, the angle of incidence at which parallel light guided to the second light guide section enters reflective surface of saw teeth at positions away from the LED is set to be greater than the angle of incidence (δ) at which the light enters the reflective surface of the saw teeth at the side toward the LED. In addition, in the prism section, the angle of protrusion of the saw teeth at positions away from the LED is set to be greater than the angle of protrusion of the saw teeth at the side toward the LED.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage application of International ApplicationNo. PCT/JP2009/006157, filed on Nov. 17, 2009. Priority under 35 U.S.C.119(a) and 35 U.S.C. 365(b) is claimed from Japanese Application No. JP2008-294059, filed Nov. 18, 2008, the disclosure of which is alsoincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element and a light emittingdevice. 2. Description of Related Art

In these years, LED lighting devices are coming into practical use inaccordance with the development of high power LEDs (Light EmittingDiodes) and high efficiency LEDs as alternatives to incandescentlight-bulbs and fluorescent lamps. Being compared with an incandescentlight-bulb and a fluorescent lamp, an LED is small in its size and highin the luminous density. Furthermore, while the incandescent light-bulband fluorescent lamp emit light in all the directions, the LED isprovided with a feature of having a narrow directivity of its light.Moreover, recently power LEDs with their capacity of 3 W and even thosewith the capacity of 10 W have been also coming into practical use.

As a plane lighting unit using such an LED for a light source, proposedis a plane lighting device described below. Specifically, a lightguiding plate includes a light incoming section for guiding light froman LED, a surface section for emitting the light, a rear surface sectionlocated at a side opposite to the surface section, and a side sectionconnecting the surface section and the rear surface section; in whichthe light incoming section is located at a position inner than the sidesection, and optical elements (prisms) provided with tilted surfacescorresponding to a bundle of light coming from the LED are placed in thesurface section continuously at positions corresponding to a brightnessdistribution or an optical energy distribution of a light source. Theprisms are provided with a density distribution increasing functionallyin proportion to a distance from the LED (Refer to Patent Document 1).

In the plane lighting device described in Patent Document 1, intervalsof the prisms, or a distribution of the prisms in other words, aredense, for example at a light guiding section that is located distantfrom the LED and likely to have a low brightness. Through such anarrangement, a uniform brightness and a uniform energy emission areachieved at the emission side, and light can be emitted in such a waythat a product of an amount of emitted light and an emission light angleis uniform at any position in the light guiding plate.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP2007-234617 A

SUMMARY OF THE INVENTION

Unfortunately, in the case of such a plane lighting device described inPatent Document 1, directional characteristics of light are strong, anda light illumination area is not wide enough. Therefore, the planelighting device described in Patent Document 1 is preferred forbacklighting a liquid-crystal-display of mobile equipment, such as acellular phone, an electronic data-book, a mobile personal computer, andthe like. In the meantime, when being used for another purpose, such aslighting, the plane lighting device described in Patent Document 1 needsto widen a light emission area for outgoing light in the light guidingsection in order to have a wide light illumination area. Therefore,widening the area leads to a large-sized device and a high-priced deviceas well.

Thus, it is an object of the present invention to provide an opticalelement and a light emitting device that makes it possible to widen alight illumination area despite a small-sized light emission area fordownsizing the device.

To achieve the object described above, an optical element according tothe present invention comprises a plate-like light guiding section forguiding light, in which the light guiding section includes, on a surfaceof one side thereof, a prism section the cross-sectional shape of whichis composed of a plurality of saw teeth for changing travelingdirections of the light guided by the light guiding section, theincident angle at which parallel light guided by the light guidingsection enters reflective surfaces of the saw teeth at positions awayfrom a light entry side being larger than the incident angle at whichthe parallel light guided by the light guiding section enters reflectivesurfaces of the saw teeth at the light entry side.

To achieve the object described above, an optical element according tothe present invention comprises a plate-like light guiding section forguiding light, in which the light guiding section includes, on a surfaceof one side thereof, a prism section the cross-sectional shape of whichis composed of a plurality of saw teeth for changing travelingdirections of the light guided by the light guiding section, theprotrusion angle of the saw teeth at positions away from a light entryside of the light guided by the light guiding section being larger thanthe protrusion angle of the saw teeth at positions at the light entryside.

It is preferable that the further from the position of the light entryside toward the distant position a location is, the larger graduallyeither of the incident angle of light entering the reflective surfacesof the saw teeth or the protrusion angle of the saw teeth is made at thelocation.

It is preferable that a reflecting part is provided at an edge side ofthe prism section, located to be distant from the light entry side ofthe light guiding section; the reflecting part reflecting the lightguided by the light guiding section in the same direction as the prismsection changes the traveling directions of the light.

It is preferable that the saw teeth are placed concentrically; and thesaw teeth are placed concentrically; and one part of the prism sectionat the light entry side is located closer to a center of the concentriccircles and another part of the prism section at the distant position islocated further from the center of the concentric circles.

It is preferable that the light guiding section is made of a translucentresin material, and the light guiding section contains light scatteringparticles, while the light scattering particles are translucent siliconparticles having their particle diameter within a range from 1 to 10 nm.

To achieve the object described above, a light emitting device accordingto the present invention comprises a plate-like light guiding sectionfor guiding light, and a light emitting component for emitting thelight: in which the light guiding section includes, on a surface of oneside thereof, a prism section the cross-sectional shape of which iscomposed of a plurality of saw teeth for changing traveling directionsof the light guided by the light guiding section, the incident angle atwhich parallel light guided by the light guiding section entersreflective surfaces of the saw teeth at positions away from the lightemitting component being larger than the incident angle at which theparallel light guided by the light guiding section enters reflectivesurfaces of the saw teeth at the position near the light emittingcomponent.

To achieve the object described above, a light emitting device accordingto the present invention comprises a plate-like light guiding sectionfor guiding light, and a light emitting component for emitting thelight: in which the light guiding section includes, on a surface of oneside thereof, a prism section the cross-sectional shape of which iscomposed of a plurality of saw teeth for changing traveling directionsof the light guided by the light guiding section, the protrusion angleof the saw teeth at positions away from the light emitting componentbeing larger than the protrusion angle of the saw teeth at positions atthe position near the light emitting component.

It is preferable that the further from the position of the side of thelight emitting component toward the distant position a location is, thegreater gradually either of the incident angle of light entering thereflective surfaces of the saw teeth or the protrusion angle of the sawteeth is made at the location.

According to the present invention, provided can be an optical elementand a light emitting device that makes it possible to widen a lightillumination area despite a small-sized light emission area fordownsizing the device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view drawing to show a structure of a translucentmember as an optical element according to an embodiment of the presentinvention.

FIG. 2 is a front elevation view of the translucent member shown in FIG.1.

FIG. 3 is a bottom plan view of the translucent member shown in FIG. 1.

FIG. 4 is a cross-sectional view taken from the line A-A of the planview of FIG. 1.

FIG. 5 is an enlarged view showing details of a part of a reflectingsurface of the translucent member shown in the cross-sectional view ofFIG. 4.

FIG. 6 is a graph showing an angle distribution (A, Θ) of a scatteredlight intensity by a single spherical particle.

FIG. 7 is an enlarged general view showing a main part of a second lightguiding section of the translucent member shown in the cross-sectionalview of FIG. 4.

FIG. 8 shows a structure of a light emitting device according to theembodiment of the present invention.

FIG. 9 shows paths through which rays of light emitted from an LED enterthe translucent member, and then the rays are reflected at thereflecting surface so as to be guided to the second light guidingsection, in the light emitting device according to the embodiment of thepresent invention.

FIG. 10 shows a brightness distribution in a light emitting device of afirst modification with respect to the light emitting device accordingto the embodiment of the present invention.

FIG. 11 shows a brightness distribution in a light emitting device of asecond modification with respect to the light emitting device accordingto the embodiment of the present invention.

FIG. 12 shows a brightness distribution in the light emitting deviceaccording to the embodiment of the present invention.

FIG. 13 shows a brightness distribution in a light emitting device of athird modification with respect to the light emitting device accordingto the embodiment of the present invention.

FIG. 14 is a graph showing a relationship between a light divergenceangle and a light transmission factor as a density of light scatteringparticles varies; wherein the light scattering particles, used for thelight emitting device according to the embodiment of the presentinvention, being contained in an acrylic resin plate with a thickness of10 mm

FIG. 15 is a plan view drawing to show a first modification of thetranslucent member according to the embodiment of the present invention.

FIG. 16 is a drawing to show an example of using a light emitting deviceapplying the translucent member shown in FIG. 15 as a street lamp, thedrawing showing a view from a road side.

FIG. 17 is a drawing to show the example of using the light emittingdevice applying the translucent member shown in FIG. 15 as the streetlamp, the drawing showing a view in a traveling direction.

FIG. 18 is a plan view drawing to show a second modification of thetranslucent member according to the embodiment of the present invention.

FIG. 19 is a side elevation view of the translucent member of the secondmodification shown in FIG. 18, the side elevation view showing a viewtaken from a direction of a large arrow “C” in FIG. 18.

FIG. 20 is a side elevation view of the translucent member of the secondmodification shown in FIG. 18, the side elevation view showing a viewtaken from a direction of a large arrow “B” in FIG. 18.

FIG. 21 is a schematic cross-sectional view of a sign applying a lightemitting device using the translucent member of the second modification,as a light source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Structures and functions of an optical element and a light emittingdevice according to an embodiment of the present invention are describedbelow with reference to the accompanied drawings.

(Structure of Optical Element)

FIG. 1 is a plan view drawing to shows a structure of a translucentmember 1 as an optical element according to an embodiment of the presentinvention, and in the meantime, FIG. 2 and FIG. 3 are a front elevationview and a bottom plan view of the translucent member, respectively.

As shown in FIGS. 1 to 3, having its circular contour, the translucentmember 1 is a transparent poly-methyl methacrylate (hereinafterabbreviated to “PMMA”) resin compact that contains spherical andtranslucent silicone particles (not illustrated) with their particlediameter of several micro-meters, as light scattering particles. Thetranslucent member 1 includes a first light guiding section 2 positionedat a central area, and being flat and circular-shaped; and a secondlight guiding section 3 positioned around the first light guidingsection 2, and being torus or doughnut-shaped. The first light guidingsection 2 includes a light incoming section 11 through which lightenters the first light guiding section 2 (Refer to FIG. 3 and FIG. 4),and a reflecting surface 12 that reflects the incident light on thelight incoming section 11, and is located at a surface opposite to thelight incoming section 11.

Positioned at a center of the reflecting surface 12 is a center point13, which is a center of the translucent member 1, and a center of thefirst light guiding section 2, as well as a center of the second lightguiding section 3. In the translucent member 1, the incident light onthe light incoming section 11 is guided to the reflecting surface 12,and then the light reflected by the reflecting surface 12 is guided tothe second light guiding section 3. The first light guiding section 2and the second light guiding section 3 are integrated into a whole insuch a manner that the translucent member 1 is so made as to look likejust a wholly-integrated single component. In the following explanation,an upper side and a lower side in FIG. 2 are called a topside and abottom side of the translucent member 1, respectively.

The first light guiding section 2 shown in FIG. 1 has its outer radius(R1) of 11 mm, meanwhile the second light guiding section 3 has itsouter radius (R2) of 80 mm. Therefore, in the translucent member 1, anarea that the first light guiding section 2 occupies is calculated froma formula (πR¹²/πR²²) to be approximately 1.89%.

As shown in FIG. 2, a topside surface of the second light guidingsection 3 of the translucent member 1 is a flat surface, meanwhile abottom side surface of the second light guiding section 3 is so formedas to slope from an edge 15 of the translucent member 1 toward the firstlight guiding section 2 positioned at the center of the translucentmember 1 to gradually increase the thickness of the second light guidingsection 3. Then, at a lower side of the edge 15 of the translucentmember 1, there is formed a ring-shaped reflecting part 16 that fullyreflects upward the light guided into the second light guiding section3. The reflecting part 16 is placed in a concentric pattern having itscenter at the center point 13. In the meantime, the first light guidingsection 2 has an LED holder 17, shaped to be cylindrical, at its bottomside.

As shown in FIG. 3, the circular first light guiding section 2 islocated at a central area of the translucent member 1; and the LEDholder 17, being ring-shaped, is located at a bottom side of the firstlight guiding section 2. In the meantime, the reflecting part 16, beingring-shaped, is formed with a uniform shape at each location along anentire circumference at a bottom side of the edge 15 of the second lightguiding section 3.

FIG. 4 is a cross-sectional view taken from the line A-A of the planview of FIG. 1. The LED holder 17 is shaped to be cylindrical, beingprotruded toward a bottom side. Though constituting a part of the firstlight guiding section 2, the LED holder 17 may be placed at a bottomside of the second light guiding section 3, being formed as a part ofthe second light guiding section 3. An inner-circumferential surface 17a of the LED holder 17 stretches to a bottom side, being perpendicularto a flat surface of the light incoming section 11. In the meantime, anouter-circumferential surface 17 b of the LED holder 17 is so formed asto make an acute angle “α” with respect to the inner-circumferentialsurface 17 a. When light coming from a light source to be describedlater enters the LED holder 17, the outer-circumferential surface 17 breflects incident light and guides the light toward the first lightguiding section 2 and the second light guiding section 3.

FIG. 5 is an enlarged view showing details of a surrounding part of thereflecting surface 12 of the translucent member 1 shown in thecross-sectional view of FIG. 4. A most concave part in the reflectingsurface 12 has the center point 13. Incidentally, the translucent member1 shown in FIG. 5 contains light scattering particles 21. The lightscattering particles 21 are silicone particles with their particlediameter of 1 to 10 μm, and are contained with a higher density in thefirst light guiding section 2 than in the second light guiding section3. More specifically, a content rate of the light scattering particles21 in the first light guiding section 2 is 0.1 weight percent, meanwhilethat in the second light guiding section 3 is 0.06 weight percent.Incidentally, where a scattering parameter and a thickness of the firstlight guiding section 2 are expressed as “τ” and “T”, respectively, theproduct of “τ” and “T” with respect to the light scattering particles 21contained in the first light guiding section 2 is within a range of 0.1to 50.

In the present embodiment, the LED holder 17 also contains the lightscattering particles 21, and a content rate of the light scatteringparticles 21 there is the same as that in the first light guidingsection 2. However, it is also possible for the LED holder 17 to containno light scattering particles 21 or to have the same content rate of thelight scattering particles 21 as that in the second light guidingsection 3. FIG. 5 shows that the light scattering particles 21 areplaced in a dispersed state.

The light scattering particles 21 are further described next. The lightscattering particles 21 are light guiding elements provided with auniform scattering power within their volume-wise extent, and theyinclude a number of spherical particles as scattering fine particles.When light enters an internal area of the first light guiding section 2or the second light guiding section 3, the light is scattered by thescattering fine particles.

The Mie scattering theory that provides the theoretical fundamentals ofthe light scattering particles 21 is explained next. Calculated in theMie scattering theory is a solution for Maxwell's equations ofelectromagnetism in the case where spherical particles (scattering fineparticles) exist in a ground substance (matrix) having a uniformrefractive index, wherein the spherical particles having a refractiveindex that is different from the refractive index of the matrix. Aformula (1) described below expresses a light intensity distribution I(Λ, Θ) dependent on scatting angles of light scattered by scatteringfine particles that correspond to the light scattering particles 21. “A”is a size parameter representing an optical size of the scattering fineparticles, and the parameter shows an amount corresponding to a radius“r” of the spherical particles (the scattering fine particles)standardized with a wavelength “λ” of light in the matrix. Meanwhile, anangle “Θ” represents a scattering angle, wherein a direction identicalto a traveling direction of incident light corresponds to “Θ=180 deg.”

“i1” and “i2” in the formula (1) are expressed with formulas (4). Then,“a” and “b” subscripted with “ν” in formulas (2) to (4) are expressedwith formulas (5). P(cos Θ) superscripted with “1” and subscripted with“ν” is a Legendre polynomial; meanwhile “a” and “b” subscripted with “ν”are composed of a first kind Recatti-Bessel function Ψ_(ν), a secondkind Recatti-Bessel function ζ_(ν), and their derivatives. “m” is arelative refractive index of the scattering fine particles withreference to the matrix, namely “m=n-scatter/n-matrix.”

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{{I\left( {A\; \Theta} \right)} = {\frac{\lambda^{2}}{8\pi^{2}}\left( {i_{1} + i_{2}} \right)}} & (1) \\{{K(A)} = {\left( \frac{2}{\alpha^{2}} \right){\sum\limits_{v = 1}^{\infty}{\left( {{2v} + 1} \right)\left( {{a_{v}}^{2} + {b_{v}}^{2}} \right)}}}} & (2) \\{A = {2\pi \; {r/\lambda}}} & (3) \\{{i_{1} = {{\sum\limits_{v = 1}^{\infty}{\frac{{2v} + 1}{v\left( {v + 1} \right)}\left\{ {{a_{v}\frac{P_{v}^{1}\left( {\cos \; \Theta} \right)}{\sin \; \Theta}} + {b_{v}\frac{{P_{v}^{1}\left( {\cos \; \Theta} \right)}}{\Theta}}} \right\}}}}}{i_{2} = {{\sum\limits_{v = 1}^{\infty}{\frac{{2v} + 1}{v\left( {v + 1} \right)}\left\{ {{b_{v}\frac{P_{v}^{1}\left( {\cos \; \Theta} \right)}{\sin \; \Theta}} + {a_{v}\frac{{P_{v}^{1}\left( {\cos \; \Theta} \right)}}{\Theta}}} \right\}}}}}} & (4) \\{{a_{v} = \frac{{{\Psi_{v}^{\prime}\left( {m\; A} \right)}{\Psi_{v}(A)}} - {m\; {\Psi_{v}\left( {m\; A} \right)}{\Psi_{v}^{\prime}(A)}}}{{{\Psi_{v}^{\prime}\left( {m\; A} \right)}{\zeta_{v}(A)}} - {m\; {\Psi_{v}\left( {m\; A} \right)}{\zeta_{v}^{\prime}(A)}}}}{b_{v} = \frac{{m\; {\Psi_{v}^{\prime}\left( {m\; A} \right)}{\Psi_{v}(A)}} - {{\Psi_{v}\left( {m\; A} \right)}{\Psi_{v}^{\prime}(A)}}}{{m\; {\Psi_{v}^{\prime}\left( {m\; A} \right)}{\zeta_{v}(A)}} - {{\Psi_{v}\left( {m\; A} \right)}{\zeta_{v}^{\prime}(A)}}}}} & (5)\end{matrix}$

FIG. 6 is a graph showing a light intensity distribution I (A, Θ) by asingle spherical particle on the basis of the above formulas (1) to (5).Namely, FIG. 6 shows an angular distribution of scattered lightintensity I (A, Θ) in the case of incident light coming in from a lowerside, wherein a spherical particle as a scattering fine particle existsat a position of an origin “G” In the figure, a distance from the origin“G” to each of curves S1 to S3 represents the scattered light intensityin a corresponding angular direction of the scattered light. Each curveof S1, S2, and S3 shows the scattered light intensity when the sizeparameter “A” is 1.7, 11.5, and 69.2, respectively. In FIG. 6, thescattered light intensity is expressed in a logarithmic scale.Therefore, even a slight difference of intensity that appears in FIG. 6is a significantly large difference in fact.

As shown FIG. 6, it is understood that; the larger the size parameter“A” is (the larger the particle diameter is, at a certain wavelength“λ”), the more intensively the light is scattered in an upward direction(a frontward direction in the direction of radiation) with highdirectivity. In reality, the angular distribution of scattered lightintensity I (A, Θ) can be controlled by using the radius “r” of thescattering element and the relative refractive index “m” between thematrix and the scattering fine particles as parameters, while thewavelength “λ” of incident light is set to be constant.

Thus, when incident light enters a scatter light guiding element thatcontains N (in number) single spherical particles, the incident light isscattered by a spherical particle. Moving forward through the scatterlight guiding element, the scattered light is then scattered again byanother spherical particle. In the case where particles are added with acertain volume concentration or higher, such scattering operationsequentially repeats several times and then the light is launched out ofthe scatter light guiding element. A phenomenon, in which such ascattered light is further scattered, is called a multiple scatterphenomenon. Though it is not easy to analyze such a phenomenon ofmultiple scattering in a translucent polymer substance by means of a raytracing method, the behavior of a ray can be traced by Monte Carlomethod for analysis of its characteristics. According to the analysis,in the case of incident light having no polarization, a cumulativedistribution function of scattering angle “F(Θ)” is expressed with aformula (6) described next.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{{F(\Theta)} = \frac{\int_{0}^{\Theta}{{I(\Theta)}\sin \; \Theta {\Theta}}}{\int_{0}^{\pi}{{I(\Theta)}\sin \; \Theta {\Theta}}}} & (6)\end{matrix}$

“I(Θ)” in the formula (6) means the scattered light intensity of thespherical particle of the size parameter “Λ” expressed in the formula(1). When light having an intensity “I₀” enters the scatter lightguiding element, and transmits for a distance “y” so as to be attenuatedinto “I” through the scattering, a formula (7) described belowrepresents a relationship of the phenomenon.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{\frac{I}{I_{0}} = {\exp \left( {{- \tau}\; y} \right)}} & (7)\end{matrix}$

“τ” in the formula (7) is called the turbidity (having the same meaningas the “scattering parameter” mentioned previously); and it correspondsto a scattering coefficient of the matrix, and being proportional to thenumber of particles “N”, as a formula (8) indicates below. In theformula (8), “σ^(s)” represents a scattering cross-section area.

[Expression 4]

τ=σ^(s)N   (8)

According to the formula (7), the probability “p_(t)(L)” of transmissionpassing through the scatter light guiding element having its length “L”without any scattering is expressed by a formula (9) described below.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{{p_{t}(L)} = {\frac{I}{I_{0}} = {\exp \left( {{- \sigma^{s}}{NL}} \right)}}} & (9)\end{matrix}$

On the contrary, the probability “p_(s)(L) of having any scatteringwithin the optical path length “L” is expressed by a formula (10)described below.

[Expression 6]

p _(s)(L)=1−p _(s)(L)=1−exp(−σ² NL)   (10)

It is understood according to the formulas described above thatadjusting the turbidity “τ” makes it possible to control a degree ofmultiple scattering in the scatter light guiding element.

As the formulas indicate above, by using at least one of the sizeparameter “A” and the turbidity “τ” with respect to the scattering fineparticles as a parameter, it becomes possible to control multiplescattering in the scatter light guiding element, and also to suitablyset the launching light intensity and the scattering angle at alaunching surface.

FIG. 7 is an enlarged general view showing mainly a part of the secondlight guiding section 3 of the translucent member 1 shown in thecross-sectional view of FIG. 4. The second light guiding section 3 has aprism section 22 at its bottom side, the prism section 22 having itssawtooth-like section and being placed on a circle concentric with thecenter point 13. In the present embodiment, a total of 225 saw teeth 23are formed in the prism section 22. Incidentally, only 25 in total ofthe saw teeth 23 are shown in FIG. 7 for the purpose of simpleindication. The prism section 22 changes a course of light guided to abottom side of the second light guiding section 3 to a topside.Meanwhile, a protrusion angle θ of a saw tooth 23 located at a positioncloser to the center point 13 is acuter than a protrusion angle θ ofanother saw tooth 23 located at a position further from the center point13.

Protrusion angles θ of the saw teeth 23 are specifically explainedbelow. A protrusion angles θ of 25 saw teeth 23 existing within a widthof 5 mm being closest to the center point 13 is 50 degrees. A protrusionangles θ of 25 saw teeth 23 existing within a width of 5 mm being nextcloser to the center point 13 is 55 degrees. A protrusion angles θ of 25saw teeth 23 existing within a width of 5 mm being next closer to thecenter point 13 is 60 degrees. A protrusion angles θ of 25 saw teeth 23existing within a width of 5 mm being next closer to the center point 13is 65 degrees. A protrusion angles θ of 50 saw teeth 23 existing withina width of 10 mm being next closer to the center point 13 is 70 degrees.A protrusion angles θ of 75 saw teeth 23 existing within a width of 15mm being furthest from the center point 13 is 75 degrees.

Thus, the prism section 22 includes 5 divided groups of saw teeth 23;and the further from the center point 13 toward the edge 15 each groupof teeth is located, the larger gradually the protrusion angle θ and anincident angle δ for the group of teeth are made. Namely, in the prismsection 22, an incident angle δ of light at a position distant from alight entry side (a side of the edge 15) is larger than an incident δ ata position of the light entry side (a side of the center point 13),while the parallel light guided by the second light guiding section 3entering reflective surfaces 24 of the saw teeth 23 at the incidentangle δ of each corresponding position. Then, in the prism section 22, aprotrusion angle θ of the saw teeth 23 at a position distant from thelight entry side is larger than a protrusion angle θ of the saw teeth ata position of the light entry side, while the light guided by the secondlight guiding section 3 entering from the light entry side.Incidentally, the further outward an individual tooth 23 is located, thelarger gradually the protrusion angle θ of the saw tooth 23 may be made.In the meantime, a distance ‘H’ between neighboring two saw teeth 23 is0 2 mm, and the saw teeth 23 are placed to be symmetrical with respectto the center point 13.

In FIG. 7, a crossing angle β formed by a line “L” connecting protrusionpeaks of the saw teeth 23 in a radial direction and the topside surfaceof the second light guiding section 3 is 6.5 degrees. Though an angle γformed by a surface, at a closer side to the center point 13, of each ofthe saw teeth 23 and the line “L” is 90 degrees, the angle γ may be setto be larger than 90 degrees. If the angle γ is set to be larger, thetranslucent member 1 can more easily be removed from a mold after thetranslucent member 1 is formed with the mold. Incidentally, at the lowerside of the edge 15 adjacent to a saw tooth 23 located at the furthestposition from the center point 13, there is placed the reflecting part16. An angle θ₁ formed by a surface of the reflecting part 16 and thetopside surface of the second light guiding section 3 is 30 degrees.

(Structure of Light Emitting Device)

FIG. 8 shows a structure of a light emitting device 40 according to theembodiment of the present invention, the light emitting device 40 havinga chip-shaped LED 30 functioning as a light emitting component placed inthe translucent member 1 shown in FIG. 4. The LED 30 is placed in asection surrounded by the light incoming section 11 and the LED holder17 of the translucent member 1. A bottom part 31 of the LED 30 is shapedlike a disc so that its circumferential surface 32 faces theinner-circumferential surface 17 a of the LED holder 17. Thecircumferential surface 32 of the bottom part 31 and theinner-circumferential surface 17 a of the LED holder 17 are fixed toeach other with a fixing member that is not illustrated. By means offixing that part, the LED 30 is fixed to the LED holder 17. In themeantime, the LED 30 is located at a position facing the center point13.

(Condition of Light Reflection at Reflecting Surface 12)

FIG. 9 shows light paths, with dotted lines, through which rays of lightemitted from the LED 30 enter the light incoming section 11 to get intothe translucent member 1, and then the light is reflected at thereflecting surface 12 so as to be guided to the second light guidingsection 3. When the light emitted from the LED 30 enters the first lightguiding section 2 through the light incoming section 11, the light isrefracted somewhat in a direction toward the center point 13, and thenarrives at the reflecting surface 12. Incidentally, an interface betweenPMMA as a substance of the translucent member 1 and the atmosphere isformed at the reflecting surface 12. When light is radiated to thereflecting surface 12 with an incident angle θ₂ with respect to theinterface (namely, the reflecting surface 12) while the incident anglebeing larger than a total reflection critical angle (41.84 degrees); thelight, traveling from a medium having a higher optical refractive index(PMMA) to another medium having a lower optical refractive index (theatmosphere), does not pass through the interface, but is totallyreflected there. On this occasion, the incident angle θ₂ is an angleformed between a normal line at a point, where incident light arrives atthe reflecting surface 12, and the incident light. The reflectingsurface 12 is so formed as to satisfy the condition for such a totalreflection, and furthermore to make the reflected light travel inparallel with the topside surface of the second light guiding section 3.Therefore, most of light emitted from the LED 30 is totally reflected atthe reflecting surface 12 so as to become parallel light, and is guidedto the second light guiding section 3.

In the meantime, on a profile curve of the reflecting surface 12 shownin FIG. 9, a point corresponding to the center point 13 has a surfacewhere a sum of an incident angle and a reflection angle becomes 90degrees for light emitted straight upward from the LED 30 as a lightsource. In other words, an incident angle θ₂ for the point correspondingto the center point 13 is 45 degrees (an angle θ_(t1) as a sum of theincident angle and reflection angle there is equal to 90 degrees); and atangential line on the reflecting surface 12 at the reflection pointthere intersects the topside surface of the second light guiding section3 with an angle of 45 degrees. On the other hand, at a point where theprofile curve of the reflecting surface 12 meets a plane of the topsidesurface of the second light guiding section 3, an angle θ_(t2) as a sumof the incident angle and reflection angle there is described as“θ_(t2)=90 degrees+θ_(c)” (wherein the angle θ_(c) is the totalreflection critical angle; i.e., 41.84 degrees). A curve F(x) connectingthese two points described above is a parabolic curve, as a kind ofaspheric curve; and its derivative F′(x) is expressed as “tan(90−θt/2).”

Incidentally, the translucent member 1 contains the light scatteringparticles 21. Therefore, in a course from emission out of the LED 30through entering the first light guiding section 2 to reaching thereflecting surface 12, and another course from reflection at thereflecting surface 12 to being guided into the second light guidingsection 3, the light is scattered. Since the light scattering particles21 multiply-scatter most of the light within the translucent member 1without attenuation, a part of the incident light passes through thereflecting surface 12 of the first light guiding section 2 to exitupward. In the meantime, the size of the light scattering particles 21is adjusted according to the Mie scattering theory so as to increase theproportion of scattering in a traveling direction of the incident light,and therefore most of the light travels through almost the same path asthey do without the light scattering particles 21. In other words, mostof the light that enters the light incoming section 11 travels along thedotted lines with an arrow shown in FIG. 9 from the first light guidingsection 2 toward the second light guiding section 3 as almost parallellight.

In the operation described above, the light scattering particles 21 makea part of the light emitted from the LED 30 pass through the reflectingsurface 12, and generate light that exits outside. Namely, a past of thelight emitted from the LED 30 exits upward from the first light guidingsection 2.

(Condition of Light Refraction and Reflection in the Second LightGuiding Section 3)

As described above, the light guided into the second light guidingsection 3 changes their traveling directions toward the topside surfaceof the second light guiding section 3 by the prism section 22 and thereflecting part 16. The line “L” (Refer to FIG. 7) connecting theprotrusion peaks of the saw teeth 23 of the prism section 22 is soformed as to make the crossing angle β by intersecting the optical pathsof rays of the light guided into the second light guiding section 3.Therefore, the guided parallel light is radiated to the prism section22.

The light radiated to the prism section 22 changes the travelingdirection toward the topside surface of the second light guiding section3. With regard to the changed traveling direction, an output angle θ₃ atan outer circumferential position becomes smaller, because a protrusionangle θ at the outer circumferential position is larger in thetranslucent member 1. That is to say; when being applied as a lightsource, the translucent member 1 works as a light source withoutdirectivity for illuminating a wide-angled area (Refer to FIG. 7). Sincethe light traveling through the second light guiding section 3 is partlyscattered by the light scattering particles 21, a part of the lightradiated to the prism section 22 may pass through a saw tooth 23 thatthe light collides with at first, but most of the light that has passedthrough there at first is radiated to a neighboring saw tooth 23 so asto change its traveling direction toward the topside surface of thesecond light guiding section 3 by the saw tooth 23. Incidentally, thedotted lines with an arrow shown in FIG. 7 indicate optical paths ofrays of the light that change their traveling directions when no lightscattering particles 21 exist, or when the light does not collide withthe light scattering particles 21.

As described above, the protrusion angle θ of a saw tooth 23 is larger,as the saw tooth 23 is located to be further from a side of the LED 30toward the edge 15 of the second light guiding section 3 within an areaof the second light guiding section 3. Due to the arrangement, asdescribed above, the light that changes its traveling direction isemitted from the topside surface of the second light guiding section 3with a smaller output angle θ₃, as the emitting position is located tobe further from the side of the LED 30.

Furthermore, the light guided to the reflecting part 16 is reflected bythe reflecting part 16, and then guided toward the topside surface ofthe second light guiding section 3, and eventually emitted from thetopside. The LED 30 has a strong optical directivity. Then, lighttraveling in a direction toward the center point 13 is strong, and lighttraveling in a direction away from the center point 13 is weak.Therefore, in FIG. 7, quantity of light is lager for light guided from alower area of the reflecting surface 12 (an area close to the centerpoint 13) and an intermediate area of the reflecting surface 12 (an areasomewhat away from the center point 13), and in the meantime quantity oflight is smaller for light guided from an upper area of the reflectingsurface 12 (an area close to the second light guiding section 3) as thearea is located to be higher. Thus, the prism section 22 for mainlychanging traveling direction of light guided to the lower area and theintermediate area of the reflecting surface 12 changes travelingdirection of most of light radiated from the LED 30, and the reflectingpart 16 changes traveling direction of residual light. By means of theoperation described above, eventually most of the light travelingthrough the second light guiding section 3 are emitted from the topside.

Incidentally, the second light guiding section 3 also contains the lightscattering particles 21. Therefore, in a traveling process of the lightentering the second light guiding section 3 from the reflecting surface12 and traveling further, and also in a traveling process of the lightradiated from the prism section 22 toward the topside of the secondlight guiding section 3, the light is scattered in a complex manner.Then, the light scattering particles 21 multiply-scatter most of thelight within the second light guiding section 3 in the same direction asthe incident direction. Therefore, most of the light has the sametraveling direction so that the light is radiated along the dotted linesshown in FIG. 7. In the meantime, a part of the scattered light followsother path, being different from the dotted lines of FIG. 7, and isemitted from the topside. Specifically, the second light guiding section3 contains the light scattering particles 21 in a high dense state.Therefore, light from the topside surface of the translucent member 1 isradiated in a fading-bright condition, being different from light comingout of an LED, a naked light bulb, and the like. Furthermore, lightemitted from the LED 30, working almost like a point light source, istransformed into those of a surface light source by the first lightguiding section 2 and the second light guiding section 3, and thereforethe quantity of light radiation per unit area becomes less.

Advantageous Effect Achieved by the Embodiment of the Present Invention

The translucent member 1 and the light emitting device 40 have the firstlight guiding section 2 equipped with the reflecting surface 12.Therefore, while most of the light that enters the light incomingsection 11 travels along the dotted lines with an arrow shown in FIG. 9from the first light guiding section 2 toward the second light guidingsection 3 as almost parallel light, the light is suitably scattered inother directions. Accordingly, the translucent member 1 and the lightemitting device 40 that are suitable for surface luminescence can beprovided, suppressing the appearance of glare parts and dark sections.

More specifically, it can be said that the translucent member 1 and thelight emitting device 40 do not allow most of light, emitted upwardlinearly from the LED 30, to pass through but totally-reflect it; andfurthermore no mirror reflector intercepts light of a central area.Moreover, some of the strong light emitted from the LED 30 is soscattered as to pass through the reflecting surface 12, and thereforethe reflecting surface 12 itself works as a part of a light source. Inaddition, the second light guiding section 3 emits most of incidentlight in the same direction as the light passing through the reflectingsurface 12. Accordingly, the translucent member 1 and the light emittingdevice 40 are suitable for surface luminescence, and are also able tosuppress any appearance of an excessively glaring part. Furthermore,being able to emit most of the incident light to the topside, thetranslucent member 1 and the light emitting device 40 are provided withgood light efficiency.

A part of light that enters the first light guiding section 2 passthrough the reflecting surface 12 to form a surface light source fromthe first light guiding section 2; and the other part of residual light,as almost parallel light, enter the second light guiding section 3, andafterwards emit from the topside of the second light guiding section 3so as to form a surface light source from the second light guidingsection 3. Therefore, light radiation loss of the light emitting device40 can be restrained. Meanwhile, even if a part of light, which does notbecome almost-parallel light and enters the second light guiding section3, is radiated to the topside of the second light guiding section 3,this light is totally reflected there and not scattered. Therefore,light radiation loss of the light emitting device 40 can further berestrained. Moreover, the light totally-reflected at the topside of thesecond light guiding section 3 is afterwards reflected at the prismsection 22 in a direction according to design intent of the lightemitting device 40 so that light radiation loss of the light emittingdevice 40 can still further be restrained.

Meanwhile, since a content rate of the light scattering particles 21 inthe first light guiding section 2 is higher than in the second lightguiding section 3, the light that enters the first light guiding section2 is likely to pass through the reflecting surface 12, and accordingly alight radiation distribution of an entire part of the translucent member1 can be almost homogenized. Since a degree of multiple scattering canbe controlled by adjusting the scattering parameter “τ”, an adjustmentcan be made suitably so as to conform the brightness of the lightpassing through the reflecting surface 12 to the brightness of the lightemitted from the topside of the second light guiding section 3. FIGS. 10to 13 show brightness distributions in the light emitting device 40under conditions where the content rate of the light scatteringparticles 21 in the second light guiding section 3 is kept constant(0.06 wt. %), and meanwhile the content rate of the light scatteringparticles 21 in the first light guiding section 2 is changed. As amethod for making the content rates of the light scattering particles 21in the first light guiding section 2 and the second light guidingsection 3 different from each other, the first light guiding section 2and the second light guiding section 3 are formed in advance, while eachhaving a different content rate of the light scattering particles 21,and then afterwards the two light guiding sections are assembledtogether through integrating into a whole.

FIG. 10 shows a brightness distribution in the light emitting device 40(the light emitting device 40 of a first modification) in which thefirst light guiding section 2 contains none of the light scatteringparticles 21 (Content rate=0 wt. %). According to FIG. 10, it isunderstood that the second light guiding section 3 is brighter than thefirst light guiding section 2. A reason why some brightness can also beobserved in the first light guiding section 2 is that the LED 30 as thelight source is not a point light source, and therefore the light is notnecessarily totally-reflected and some of the light is allowed to passthrough the reflecting surface 12. Incidentally, each horizontal axis inFIGS. 10 to 13 represents distances from the center point 13, where aposition of the center point 13 is related to “0.” Diameters of thefirst light guiding section 2 and the second light guiding section 3 are22 mm and 160 mm, respectively.

FIG. 11 shows a brightness distribution in the light emitting device 40(the light emitting device 40 of a second modification) in which thefirst light guiding section 2 contains 0.03 wt. % concentration of thelight scattering particles 21, namely the concentration is a half of thecontent rate (0.06 wt. %) of the light scattering particles 21 in thesecond light guiding section 3. It is understood that the second lightguiding section 3 is a little bit brighter than the first light guidingsection 2. It is because the quantity of light passing through the lightscattering particles 21 increases as a result of scattering by the lightscattering particles 21 to increase the brightness of the first lightguiding section 2, and consequently the quantity of light that entersthe second light guiding section 3 decreases.

FIG. 12 shows a brightness distribution in the light emitting device 40in which the first light guiding section 2 contains 0.1 wt. %concentration of the light scattering particles 21, namely theconcentration is a slightly higher than the content rate (0.06 wt. %) ofthe light scattering particles 21 in the second light guiding section 3.The brightness distribution shown is that of the light emitting device40 according to the embodiment of the present invention. It isunderstood that the first light guiding section 2 and the second lightguiding section 3 have roughly equalized brightness. It is because thequantity of light passing through the reflecting surface 12 furtherincreases as a result of the light scattering particles 21 increasedmore in the first light guiding section 2, and meanwhile the quantity oflight that enters the second light guiding section 3 decreases further.

FIG. 13 shows a brightness distribution in the light emitting device 40(the light emitting device 40 of a third modification) in which thefirst light guiding section 2 contains 0.3 wt. % concentration of thelight scattering particles 21, namely the concentration is 5 timeshigher than the content rate (0.06 wt. %) of the light scatteringparticles 21 in the second light guiding section 3. It is understoodthat the first light guiding section 2 is brighter than the second lightguiding section 3.

FIG. 14 shows a relationship between a light divergence angle and alight transmission factor as a density of the light scattering particles21 varies; wherein a PMMA plate with a thickness of 10 mm contains thelight scattering particles 21 with a particle diameter of 7.3 nm. Inthis situation, the light divergence angle is an angle spread in a360-degree indication at which scattered and spread light has a half ofthe brightness at the center. As shown in FIG. 14, when the content rateof the light scattering particles 21 is 0.06 wt. %, almost no divergencehappens and the light transmission factor is around 98%. By making useof FIG. 14, the brightness of the translucent member 1 and the launchingdirection of light ray can be set in various ways.

Where a scattering parameter is expressed as “τ” (“1/τ” is a mean freepath, to be expressed in “cm”), and a thickness of the first lightguiding section 2 is expressed as “T” (expressed in “cm”), the productof “τ” and “T” with respect to the light scattering particles 21 iswithin a range of 0.1 to 50. If the product of “τ” and “T” is less than0.1, the mean free path of light rays becomes long and the amount oflight rays scattered within a distance of the thickness “T” becomes lessso that an adequate amount of light rays cannot be emitted externallyfrom the reflecting surface 12 of the first light guiding section 2.Meanwhile, if the product of “τ” and “T” is larger than 50, the meanfree path of light rays becomes short and the amount of light raysmultiply-scattered within the distance of the thickness “T” becomeslarge so that the backscatter becomes large and a frontward lighttransmission factor decreases, as shown in FIG. 14. In other words, thelight efficiency of light rays, which enter the light incoming section11 and travel along the dotted lines with an arrow shown in FIG. 9 fromthe first light guiding section 2 toward the second light guidingsection 3, becomes less.

In the prism section 22, the protrusion angle θ of a saw tooth 23positioned closer to the center point 13 is smaller than that of a sawtooth 23 positioned further from the center point 13. Therefore, at aposition further from the center point 13, light can be radiated in adirection for traveling further away from the LED 30 so that light canbe radiated in a wide-angle spread. As a result, the light emittingdevice 40 becomes appropriate for an application of lighting equipmentthat can illuminate a wide extent. Furthermore, owing to radiation in awide-angle spread, the light emitting device 40 can be made to be thin.Moreover, when the light emitting device 40 is modularized so as to beplaced in a multiple arrangement, the number of modules can be reducedbecause of radiation in a wide-angle spread, and consequently it canlead to cost reduction.

As shown in FIGS. 10, 11, 12, and 13, even a position being distant fromthe translucent member 1 is illuminated, and therefore it is obviousthat the light emitting device 40 can radiate in a wide-angle spread.

Since the protrusion angle θ can be modified arbitrarily, the way ofillumination can be changed in accordance with an application of thelight emitting device 40. The way of illumination can be made forradiating in a wide-angle spread, as described above, and contrarily itis also possible to radiate in a narrow-angle spread as a downlightdoes. In the case where the crossing angle β formed by the line “L”connecting protrusion peaks of the saw teeth 23 in a radial directionand the topside surface of the second light guiding section 3 is withina range of 2 to 10 degrees, preferably the protrusion angle θ should beset in a range of 45 to 75 degrees.

Furthermore, at the lower side of the edge 15, in the second lightguiding section 3, being distant from the LED 30, there is formed thereflecting part 16 for reflecting guided light toward the topside.Therefore, even if there remain any light, which the prism section 22alone cannot change traveling directions of, it is still possible tochange the traveling direction of such light toward the topside.

(Other Modifications)

Besides the above explanation with regard to the translucent member 1and the light emitting device 40 according to the embodiment of thepresent invention, various other modifications may be made withoutchanging the concept of the present invention.

The optical element (the translucent member 1) and the light emittingdevice 40 according to the embodiment of the present inventioncomprises: the plate-like light guiding sections (the first lightguiding section 2 and the second light guiding section 3) for guidinglight. The second light guiding section 3 includes, on a surface of oneside thereof, a prism section 22 the cross-sectional shape of which iscomposed of a plurality of saw teeth 23 for changing travelingdirections of the light guided by the second light guiding section 23.The prism 22 is formed such that the incident angle δ at which parallellight guided by the second light guiding section 3 enters reflectivesurfaces 24 of the saw teeth 23 at positions away from a light entryside is larger than the incident angle δ at which the parallel lightguided by the second light guiding section 3 enters reflective surfaces24 of the saw teeth 23 at the light entry side. The light guided by thesecond light guiding section 3 is not restricted to parallel light.Moreover, the prism section 22 may be placed at a border area betweenthe first light guiding section 2 and the second light guiding section3, or in a part of the first light guiding section 2. Furthermore, onlythe second light guiding section 3 may function as the plate-like lightguiding section.

The optical element (the translucent member 1) according to theembodiment of the present invention includes: the plate-like lightguiding sections (the first light guiding section 2 and the second lightguiding section 3) for guiding light. The second light guiding section 3includes, on a surface of one side thereof, a prism section 22 thecross-sectional shape of which is composed of a plurality of saw teeth23 for changing traveling directions of the light guided by the secondlight guiding section 3. The prism 22 is formed as the protrusion angleθ of the saw teeth 23 at positions away from a light entry side of thelight guided by the second light guiding section 3 is larger than theprotrusion angle θ of the saw teeth 23 at positions at the light entryside. The prism section 22 may be placed at a border area between thefirst light guiding section 2 and the second light guiding section 3, orin a part of the first light guiding section 2.

It is preferable that the further from the position of the light entryside toward the distant position a location is, the larger graduallyeither of the incident angle δ of light entering the reflective surfaces24 of the saw teeth 23 or the protrusion angle θ of the saw teeth 23 ismade at the location. Alternatively, there may be partly be provided sawteeth 23 mixed at a light entry side, having a larger incident angle δ,or a larger protrusion angle θ of the saw teeth 23, than at a distantposition. “An angle being made larger gradually” means a case where eachgroup of saw teeth has an angle that becomes larger on a group-by-groupbasis as described in the above embodiment, and also another case aswell where the incident angle δ, or the protrusion angle θ of each sawtooth 23, not a group of saw teeth, is made larger gradually.Furthermore, in the case where each group of saw teeth has an angle thatbecomes larger on a group-by-group basis, the number of groups may beany one of 2 groups, 4 groups, 7 groups, and so on.

It is preferable that the reflecting part 16 is provided at a side ofthe edge 15 of the prism section 22, located to be distant from thelight entry side of the second light guiding section 3; the reflectingpart 16 reflecting the light guided by the light guiding section in thesame direction as the prism section 22 changes the traveling directionsof the light. Alternatively, the reflecting part 16 may be omitted sinceit is not an essential element. Moreover, the prism section 22 may beextended to the edge 15.

It is preferable that the saw teeth 23 are placed concentrically; andthe prism section 22 at the light entry side and the prism section 22 atthe distant position correspond to a prism section 22 located closer toa center of the concentric circles and a prism section 22 locatedfurther from the center of the concentric circles, respectively.Alternatively, the second light guiding section 3 may have its contourof a polygonal shape, such as a triangular contour, a quadrilateralcontour, etc.; and furthermore it may also have an oval-figured contouras well. By the same token, the first light guiding section 2 may alsohave its contour in its plane, such as any polygonal contour, anoval-figured contour, and the like. Still further, as described later,the prism section 22 may be formed by placing polygonal shapes havingone center common to them, at intervals.

It is preferable that the light guiding sections (the first lightguiding section 2 and the second light guiding section 3) are made of atranslucent resin material, and the light guiding sections contain thelight scattering particles 21, while the light scattering particles 21are translucent silicon particles having their particle diameter withina range from 1 to 10 nm. Alternatively, the light guiding sections maynot contain the light scattering particles 21.

The optical element (the translucent member 1) according to theembodiment of the present invention comprises: the light incomingsection 11 through which light enters the first light guiding section 2for guiding the light, which have entered the light incoming section 11,to the reflecting surface 12; the reflecting surface 12, placed to beopposite to a light entry side of the first light guiding section 2, fortotally-reflecting linearly-traveling ones of the light that hasentered; and the second light guiding section 3 for guiding thereflected light; herein the first light guiding section 2 contains thelight scattering particles 21 for multiply-scattering light andgenerating light which passes through the reflecting surface 12 and areemitted externally; and the second light guiding section 3 launches atleast a part of the incoming light in a direction of the same surfaceside as the light passing through the reflecting surface 12 travel out.Alternatively, the second light guiding section 3 may also contain thelight scattering particles 21. Furthermore, the light incoming section11 includes the bottom side of the first light guiding section 2 and theLED holder 17, and the bottom side of the first light guiding section 2may include an entire section or a part of the bottom side. Moreover,the light, which the second light guiding section 3 launches, go out inthe direction of the same surface side as the light passing through thereflecting surface 12 travel out; and in this situation, a part of thelight or the entire light may be launched from the bottom side of thesecond light guiding section 3, or launched to an outer circumferenceside of the edge 15.

The optical element (the translucent member 1) according to theembodiment of the present invention has the prism section 22 at aposition, opposite to a side of the reflecting surface 12, in the secondlight guiding section 3, the prism section 22 having its sawtooth-likesection for changing traveling directions of the guided light in thedirection of the same side as the reflecting surface 12. The prismsection 22 may be placed at an upper side of the second light guidingsection 3. Moreover, not having its sawtooth-like section, the prismsection 22 may be formed as a straight line as the line ‘L’ is, or as acurved line.

The optical element (the translucent member 1) according to theembodiment of the present invention contains the light scatteringparticles 21 in the second light guiding section 3, and the content rateof the light scattering particles 21 in the first light guiding section2 is higher than that in the second light guiding section 3.Alternatively, the content rate of the light scattering particles 21 inthe first light guiding section 2 may be lower than that in the secondlight guiding section 3, or the content rate in both the sections may bethe same. Furthermore, the second light guiding section 3 may notcontain the light scattering particles 21.

With regard to the light scattering particles 21 in the optical element(the translucent member 1) according to the embodiment of the presentinvention; wherein a scattering parameter and a thickness of the firstlight guiding section 2 are expressed as ‘τ’ and ‘T’, respectively, theproduct of ‘τ’ and ‘T’ with respect to the light scattering particles 21is within a range of 0.1 to 50. Alternatively, the product of ‘τ’ and‘T’ may be outside the range, being such as 0.01, 0.05, 60, 70, 80 andthe like.

The light emitting device 40 according to the embodiment of the presentinvention comprises the light emitting component (the LED 30) emittinglight into the light incoming section 11; in which the first lightguiding section 2 contains the light scattering particles 21 formultiply-scattering light and generating light which passes through thereflecting surface 12 and are emitted externally; and the second lightguiding section 3 launches at least a part of the incoming light in adirection of the same surface side as the light passing through thereflecting surface 12 travel out.

Alternatively, the second light guiding section 3 may also contain thelight scattering particles 21. Furthermore, as the light emittingcomponent, one of a light guiding member for guiding light from a lightsource and a light reflecting member for reflecting light from a lightsource may be used instead of a light source for emitting light directlyinto the light incoming section 11.

In the light emitting device 40 according to the embodiment of thepresent invention, the second light guiding section 3 is formed to beplate-like; and placed at a center of the plate-like second lightguiding section 3 is the first light guiding section 2 that is circularin its plane. Alternatively, the second light guiding section 3 may haveits contour of a polygonal shape, such as a triangular contour, aquadrilateral contour, etc.; and furthermore it may also have anoval-figured contour as well. By the same token, the first light guidingsection 2 may also have its contour in its plane, such as any polygonalcontour, an oval-figured contour, and the like.

Used as the translucent member 1 is a component made of PMMA.Alternatively, for the member, it is also possible to use any othertranslucent resin material such as acrylic resin material, polystyrene,polycarbonate, and the like that are other kinds of polymer materials ofacrylic acid ester, or methacrylate ester, and are amorphous syntheticresin materials having high transparency, as well as glass material andso on. Though the first light guiding section 2 and the second lightguiding section 3 are assembled together through integrating later intoa whole, alternatively the translucent member 1 may be obtained byforming a wholly-integrated single component including the first lightguiding section 2 and the second light guiding section 3 from the verybeginning.

Though the light incoming section 11 is a part of the first lightguiding section 2, and flat-surfaced; alternatively the light incomingsection 11 may be formed to be convex, curved, aspheric, etc. When thelight incoming section 11 is formed to be spherical or aspheric, thecurvature may be modified arbitrarily. Furthermore, the light incomingsection 11 may be also prepared separately from the first light guidingsection 2.

The light emitting component is not limited to the LED 30, andalternatively other light emitting elements such as organicelectro-luminescence (OEL), inorganic electro-luminescence (IEL), laserluminescence, and the like may be used. Furthermore, a chip-shapedcomponent is used as the LED 30, and alternatively an LED componentequipped with a lens may be used.

Having its circular contour, the translucent member 1 includes; thereflecting surface 12 which is circular- and concave-shaped, and locatedat the center of the translucent member 1; and the second light guidingsection 3 for guiding light, which is circular-shaped, and locatedaround the reflecting surface 12. Alternatively, the contour of thetranslucent member 1, the shape of the reflecting surface 12 in itsplane, the shape of the second light guiding section 3, and the like maybe modified. For example, when the second light guiding section 3 hasits quadrilateral contour as described above, the translucent member 1can also have its quadrilateral contour. Thus, an advantage of thetranslucent member 1 having its quadrilateral contour is that thetranslucent member 1 enables placement of light-emitting faces of aplurality of light emitting devices 40 with no gap among them. In thecase of placement of the light-emitting faces in this way for their use,it becomes easy for the light-emitting faces to emit light uniformly.

The reflecting surface 12 of the translucent member 1 has a curvedsurface in such a way that a differentiation result of a functioncorresponding to its profile curve is given as a formula of “tan(90−θt/2)”, as shown in FIG. 9. Alternatively, the profile curve may bestructured with another curve according to any other conditions as faras the curve enables totally-reflection of light from the LED 30 deemedas a point light source. Furthermore, being different from a structurewith a profile curve such as an aspheric surface curve, the reflectingsurface 12 may have another kind of section with an angular shape,namely a series of straight lines connected. Namely in this case, lightreflected by the angular-shaped section may not need to form light pathsbeing almost parallel in the second light guiding section 3.

The second light guiding section 3 of the translucent member 1 includesthe prism section 22 composed of 225 saw teeth 23 which are placed onconcentric circles centered at the center point 13, and formed on thebottom surface in FIG. 7. Then, in the saw teeth 23, a protrusion angleθ of a position closer to the center point 13 is smaller than that of aposition further from the center point 13. Alternatively, a location anda shape of the prism section 22, the number of saw teeth, and aprotrusion angle θ of each saw tooth may be modified. For example, whilethe saw teeth 23 being placed on concentric circles centered at theposition of the LED 30, the translucent member 1 may have aquadrilateral contour through cutting out the edge 15 of the secondlight guiding section 3.

Though the prism section 22 is formed through placement of the saw teeth23 on the concentric circles centered at the center point 13,alternatively the saw teeth 23 may be placed on a straight line. Forexample, when a contour of the translucent member 1 is quadrilateral,the saw teeth 23 may be formed along straight lines of the quadrilateralcontour. Furthermore, the reflecting part 16 is placed fortotally-reflecting the guided light, and the part may be preparedthrough printing treatment by using white ink, or may be so made as tohave a mirror-like surface through mirror-coating, etc., by usingaluminum, silver, and the like. It is preferable that the reflectingpart 16 is so structured as to totally-reflect the guided light sincestructuring in this way eliminates any further preparation, such asprinting treatment and so on in the manufacturing step.

Though, in the present embodiment, the distance “H” between neighboringtwo saw teeth 23 is 0.2 mm, alternatively the distance “H” may bemodified so as to be set with, e.g., 0.1 mm, 0.3 mm, and so on.Furthermore, it is also possible to set the distance “H” with varyingdistance values. Namely, there may exist some different distance valuesin the translucent member 1.

The saw teeth 23 are placed on the concentric circles, and one end ofthe prism section 22 is a part of the prism section 22 at a side closerto the center of the concentric circles, while another end of the prismsection 22 is a part of the prism section 22 at a side further from theconcentric circles. Alternatively, a location and a shape of the prismsection 22 may be changed. For example, the prism section 22 may beformed to have polygonal shapes, such as quadrilateral forms and thelike, as saw teeth 23 a of a translucent member 1 a of a firstmodification of the translucent member 1 shown in FIG. 15, beingdifferent from concentric circles; the quadrilateral forms having onecenter common to them.

FIGS. 16 and 17 are drawings to show an example of using a lightemitting device 40 applying the translucent member 1 a shown in FIG. 15,as a street lamp. One end of a support post 50 is connected to a lightemitting side of the light emitting device 40, meanwhile the other endof the support post 50 is buried into the ground, and the light emittingdevice 40 illuminates an area W1 to be illuminated on the ground from anelevated position. In the area W1 to be illuminated, light from thelight emitting device 40 is spread radially and uniformly along a road51.

An area W2 to be illuminated by the light emitting device 40 in awidthwise direction of the road 51 extends radially in such a way as tocover an entire area of a width Y of the road 51. The way of extendingis to cover a wide area at a side of the road 51 and a narrow area at anoutside of the road 51, as shown in FIG. 17. This way of illumination isachieved by changing protrusion angles θ of the saw teeth 23 a placed inthe translucent member 1 a shown in FIG. 15 according to theirpositions. In other words, a protrusion angle θ of saw teeth 23 a 1positioned at an upper side in FIG. 15 is set to be smaller than that ofsaw teeth 23 a 2 positioned at a lower side. When protrusion angles areset in this way, an area to be illuminated can be controlledarbitrarily, such as making an area to be illuminated wider at the sideof the road, for example, in the case of installing a street lampapplying the light emitting device 40 at a boundary between a road and aforest.

Sometimes it may be preferable that the support post 50 is so connectedas to cover a section corresponding to the first light guiding section 2in the light emitting side of the light emitting device 40. For example,when the light emitting device 40 has a relatively non-uniformbrightness distribution as shown in FIG. 10 and FIG. 11, a relativelydark area corresponding to the first light guiding section 2 is coveredby the support post 50 so as to enable uniforming the illuminatingcondition. Furthermore, as a translucent member for illuminating aright-side area and a left-side area equally in a certain directionwhile illuminating a right-side area and a left-side area unequally in adirection perpendicular to the above-mentioned direction as shown inFIG. 16 and FIG. 17, even the translucent member 1 with a circular formas shown in FIG. 1 may be applied, being different from the translucentmember 1 a with a quadrilateral form as shown in FIG. 15.

Shown in FIG. 18 as a second modification of the translucent member 1 isa bottom plan view of a translucent member 1 b prepared by placing thesaw teeth 23 positioned on concentric circles centered at a location ofthe LED 30, and cutting out the edge 15 of the second light guidingsection 3, in order to make a contour of the translucent member 1quadrilateral (square). Each component having the same shape and thesame function as its corresponding one existing in the translucentmember 1 is provided with the same reference numeral that thecorresponding one has in FIG. 3, and an explanation on the component isomitted. A square contour section of the translucent member 1 b has anedge 15 a constituting each side part and an edge 15 b constituting eachcorner point. Each reflecting part 16 b corresponding to the reflectingpart 16 of the translucent member 1 includes 4 oval-lined part, each ofwhich is formed by swelling toward the center point 13 in a directionconnecting neighboring reflecting parts 16 along each edge 15 a.

FIG. 19 is a side elevation view of the translucent member 1 b shown inFIG. 18, taken from a direction of a large arrow “B” in the drawing.FIG. 20 is a side elevation view of the translucent member 1 b shown inFIG. 18, taken from a direction of a large arrow “C” in the drawing.Also with respect to FIG. 19 and FIG. 20, each component having the sameshape and the same function as its corresponding one existing in thetranslucent member 1 is provided with the same reference numeral thatthe corresponding one has in FIG. 3, and an explanation on the componentis omitted. An angle formed by a surface of the reflecting part 16 b andthe top surface of the second light guiding section 3 is 30 degrees, asthe angle θ is. As shown in FIG. 20, no reflecting part 16 b exists at aposition of edge 15 b.

FIG. 21 is a schematic cross-sectional view of a sign 60 including 3light emitting devices 42, each of which is a second modification of thelight emitting device 40 using the translucent member 1 b, as lightsources. On a front surface 61 b of the sign 60, there are illustratedsome characters and images, or there is placed a poster and the like.Each of the light emitting devices 42 can illuminate a wide area, andpractically illuminates an area W3. In other words, as shown in FIG. 21,the light emitting devices 42 illuminate in such a way that an area tobe illuminated by one of the light emitting devices 42 overlaps a partof that (an edge part) of a neighboring one of the light emittingdevices 42. Therefore, the sign 60 is observed as if an entire area ofthe sign 60 emits light in its illuminating direction. This illuminationstatus can be achieved even when each of the light emitting devices 42is placed, while having a clearance W4 from its neighboring lightemitting device, in the sign 60. Accordingly, in the case of the sign60, the number of light sources can be reduced dramatically, beingcompared with another case where conventionally a number of LEDs areplaced and used as light sources for a sign. As a result, the sign 60exerts its effects of reduction in power consumption, reduction in thenumber of constituent components, and so on.

FIG. 21 shows a case where 3 light emitting devices 42 are placed in avertical direction. Alternatively, 3 lines of light emitting devices inboth vertical and horizontal directions so as to have 9 light emittingdevices 42 in total may be placed for making up a sign 60 having asquare surface 61, and furthermore 3 lines by 5 lines of 15 lightemitting devices 42 in total may be placed for making up anotherrectangular sign 60. Any number of devices in vertical and horizontaldirections may be adopted arbitrarily.

REFERENCE NUMERALS

-   1, 1 a, and 1 b. Translucent member (Optical element)-   2. First light guiding section-   3. Second light guiding section-   11. Light incoming section-   12. Reflecting surface-   16, and 16 b. Reflecting part-   22, and 22 a. Prism section-   21. Light scattering particles-   30. LED-   40, 41, and 42 Light emitting device-   δ incident angle-   θ protrusion angle

1. An optical element comprising a plate-like light guiding section forguiding light in which: the light guiding section includes, on a surfaceof one side thereof, a prism section the cross-sectional shape of whichis composed of a plurality of saw teeth for changing travelingdirections of the light guided by the light guiding section, theincident angle at which parallel light guided by the light guidingsection enters reflective surfaces of the saw teeth at positions awayfrom a light entry side being larger than the incident angle at whichthe parallel light guided by the light guiding section enters reflectivesurfaces of the saw teeth at the light entry side.
 2. An optical elementcomprising a plate-like light guiding section for guiding light: inwhich the light guiding section includes, on a surface of one sidethereof, a prism section the cross-sectional shape of which is composedof a plurality of saw teeth for changing traveling directions of thelight guided by the light guiding section, the protrusion angle of thesaw teeth at positions away from a light entry side of the light guidedby the light guiding section being larger than the protrusion angle ofthe saw teeth at positions at the light entry side.
 3. The opticalelement according to claim 1: in which the further from the position ofthe light entry side toward the distant position a location is, thelarger gradually the incident angle of light entering the reflectivesurfaces of the saw teeth is made at the location.
 4. The opticalelement according to claim 1: in which a reflecting part is provided atan edge side of the prism section, located to be distant from the lightentry side of the light guiding section; the reflecting part reflectingthe light guided by the light guiding section in the same direction asthe prism section changes the traveling directions of the light.
 5. Theoptical element according to claim 1: in which the saw teeth are placedconcentrically; and one part of the prism section at the light entryside is located closer to a center of the concentric circles and anotherpart of the prism section at the distant position is located furtherfrom the center of the concentric circles.
 6. The optical elementaccording to claim 1: in which the light guiding section is made of atranslucent resin material, and the light guiding section contains lightscattering particles, while the light scattering particles aretranslucent silicon particles having their particle diameter within arange from 1 to 10 micrometers.
 7. A light emitting device comprising aplate-like light guiding section for guiding light, and a light emittingcomponent for emitting the light: in which the light guiding sectionincludes, on a surface of one side thereof, a prism section thecross-sectional shape of which is composed of a plurality of saw teethfor changing traveling directions of the light guided by the lightguiding section, the incident angle at which parallel light guided bythe light guiding section enters reflective surfaces of the saw teeth atpositions away from the light emitting component being larger than theincident angle at which the parallel light guided by the light guidingsection enters reflective surfaces of the saw teeth at the position nearthe light emitting component.
 8. A light emitting device comprising aplate-like light guiding section for guiding light, and a light emittingcomponent for emitting the light: in which the light guiding sectionincludes, on a surface of one side thereof, a prism section thecross-sectional shape of which is composed of a plurality of saw teethfor changing traveling directions of the light guided by the lightguiding section, the protrusion angle of the saw teeth at positions awayfrom the light emitting component being larger than the protrusion angleof the saw teeth at positions at the position near the light emittingcomponent.
 9. The light emitting device according to claim 7: in whichthe further from the position of the side of the light emittingcomponent toward the distant position a location is, the largergradually either of the incident angle of light entering the reflectivesurfaces of the saw teeth or the protrusion angle of the saw teeth ismade at the location.
 10. The optical element according to claim 2: inwhich the further from the position of the light entry side toward thedistant position a location is, the larger gradually the protrusionangle of the saw teeth is made at the location.
 11. The optical elementaccording to claims 2: in which a reflecting part is provided at an edgeside of the prism section, located to be distant from the light entryside of the light guiding section; the reflecting part reflecting thelight guided by the light guiding section in the same direction as theprism section changes the traveling directions of the light.
 12. Theoptical element according to claim 2: in which the saw teeth are placedconcentrically; and one part of the prism section at the light entryside is located closer to a center of the concentric circles and anotherpart of the prism section at the distant position is located furtherfrom the center of the concentric circles.
 13. The optical elementaccording to claim 2: in which the light guiding section is made of atranslucent resin material, and the light guiding section contains lightscattering particles, while the light scattering particles aretranslucent silicon particles having their particle diameter within arange from 1 to 10 micrometers.
 14. The light emitting device accordingclaim 8: in which the further from the position of the side of the lightemitting component toward the distant position a location is, the largergradually the protrusion angle of the saw teeth is made at the location.